1. Field of the Invention
The present invention relates to an optical element and an optical system using the same and, more particularly, to an optical system element suitable for, e.g., a video camera, still video camera, copying machine, and the like, and an optical system using the same.
The present invention also relates to an optical device which is used in, e.g., a silver halide camera, video camera, electronic still camera, or the like, and comprises an optical element formed integrally with a plurality of refracting surfaces and a plurality of reflecting surfaces.
2. Description of Related Art
Conventionally, as a photographing optical system, some components of which are built by reflecting surfaces, a so-called mirror optical system (reflection optical system), as shown in FIG. 12, is known.
FIG. 12 is schematic view showing principal part of a mirror optical system made up of one concave mirror and one convex mirror. In the mirror optical system shown in FIG. 12, an object light beam 104 coming from an object is reflected by a concave mirror 101, and propagates as a converging beam toward the object side. The light beam is reflected by a convex mirror 102, and thereafter, is refracted by a lens 110, thus forming an image on an image surface 103.
This mirror optical system is based on an arrangement of a so-called Cassegrainian reflecting telescope, and aims at shortening the total length of the optical system by folding the optical path of a telescope lens system with a large total lens length made up of a refraction lens using two reflecting mirrors.
In an objective lens system, such a telescope system, a large number of methods for shortening the total lengths of optical systems using a plurality of reflecting mirrors are known in addition to the Cassegrainian type for the same purpose as above.
In this manner, a compact mirror optical system is conventionally obtained by efficiently folding the optical path using a reflecting mirror in place of a lens of a photographing lens with a large total lens length.
However, in general, mirror optical systems such as a Cassegrainian reflecting telescope and the like suffer a problem that some object light rays are eclipsed by the convex mirror 102. This problem is caused by the presence of the convex mirror 102 in the passage region of the object light beam 104.
In order to solve this problem, there has also been proposed a mirror optical system that uses a decentered reflecting mirror to avoid the passage region of the object light beam 104 from being shielded by other portions of the optical system, i.e., to separate main rays of the light beam from an optical axis 105.
FIG. 13 is a schematic view showing principal part of a mirror optical system disclosed in U.S. Pat. No. 3,674,334. This optical solves the problem of eclipse using portions of reflecting mirrors which are rotationally symmetrical about the optical axis.
The mirror optical system shown in FIG. 13 includes a concave mirror 111, a convex mirror 113, and a concave mirror 112 in the passage order of a light beam, and these mirrors are originally rotationally symmetrical about an optical axis 114, as indicated by two-dashed chain lines in FIG. 13. Of these mirrors, only the upper side of the concave mirror 111, the lower side of the convex mirror 113, and the lower side of the concave mirror 112 with respect to the optical axis 114 on the plane of the drawing are used, thus constituting an optical system that separates main rays 116 of an object light beam 115 from the optical axis 114 and avoids the object light beam 115 from being eclipsed.
FIG. 14 is a schematic view showing principal part of a mirror optical system disclosed in U.S. Pat. No. 5,063,586. The mirror optical system shown in FIG. 14 solves the above problem by decentering the central axis itself of each reflecting mirror. In FIG. 14, if an axis perpendicular to an object surface 121 is defined to be an optical axis 127, central coordinates and central axes (an axis that connects the center of the reflecting surface and the center of curvature of that surface) 122a, 123a, 124a, and 125a of a convex mirror 122, a concave mirror 123, a convex mirror 124, and a concave mirror 125 in the passage order of a light beam are decentered from the optical axis 127. In this mirror optical system, by appropriately setting the decentering amounts and the radii of curvature of the individual surfaces at that time, an object light beam 128 can be prevented from being eclipsed by these reflecting mirrors, and an object image is efficiently formed on an imaging surface 126.
Also, U.S. Pat. Nos. 4,737,021 and 4,265,510 disclose an arrangement for avoiding eclipse using portions of reflecting mirrors which are rotationally symmetrical about the optical axis, and an arrangement for avoiding eclipse by decentering the central axis itself of each reflecting mirror from the optical axis.
As described above, by decentering the reflecting mirrors that build the mirror optical system, an object light beam can be avoided from being eclipsed. However, since the individual reflecting mirrors must be set to have different decentering amounts, a structure that attaches these reflecting mirrors is complicated, and it becomes very difficult to assure high alingnment precision.
As one method of solving this problem, for example, a mirror system may be formed as a block to avoid assembly errors of optical parts upon assembly.
As conventional blocks having a large number of reflecting surfaces, for example, optical prisms such as a pentagonal roof prism, a Porro prism, and the like, which are used in a finder system or the like, a color separation prism that separates a light beam coming from a photographing lens into three, i.e., red, green, and blue color light beams and forms object images based on the individual color light beams on the surfaces of corresponding image sensing elements, and the like are known.
In these prisms, since a plurality of reflecting surfaces are integrally formed, the relative positional relationship among the reflecting surfaces is accurately determined, and the positions of the reflecting surfaces need not be adjusted.
However, the principal function of such prisms is to reverse an image by changing the traveling directions of light rays, and each reflecting surface is defined by a plane.
In contrast to this, an optical system in which reflecting surfaces of a prism have curvatures is also known.
FIG. 15 is a schematic view showing principal part of an observation optical system disclosed in U.S. Pat. No. 4,775,217. This observation optical system allows an observer to observe the landscape of the outer field and also to observe an image displayed on an information display member overlapping the landscape.
In this observation optical system, a display light beam 145 originating from an image displayed on an information display member 141 is reflected by a surface 142, and propagates toward the object side. The light beam is then incident on a half mirror surface 143 defined by a concave surface. The light beam is reflected by the half mirror surface 143, and becomes a nearly collimated light beam by the refractive power of the concave surface 143. After the light beam is refracted by and transmitted through a surface 142, it forms an enlarged virtual image of the displayed image and enters the pupil 144 of the observer, thus making the observer to see the displayed image.
On the other hand, an object light beam 146 from an object is incident on and refracted by a surface 147 which is nearly parallel to the reflecting surface 142, and reaches the half mirror surface 143 as the concave surface. Since a semi-transparent film is deposited on the concave surface 143, some light components of the object light beam 146 are transmitted through the concave surface 142, are refracted by and transmitted through the surface 142, and then enter the pupil 144 of the observer. With these light components, the observer visually observes the displayed image overlapping the landscape of the outer field.
FIG. 16 is a schematic view showing principal part of an observation optical system disclosed in Japanese Patent Laid-Open Patent No. 2-297516. This observation optical system also allows the observer to observe the landscape of an outer field, and to observe an image displayed on an information display member overlapping the landscape.
In this observation optical system, a display light beam 154 originating from an information display member 150 is transmitted through a flat surface 157, that builds a prism Pa, to enter the prism Pa, and then strikes a parabolic reflecting surface 151. The display light beam 154 is reflected by the reflecting surface 151 to be converted into a converging light beam, and forms an image on a focal plane 156. At this time, the display light beam 154 reflected by the reflecting surface 151 reaches the focal plane 156 while being totally reflected by two parallel flat surfaces 157 and 158 that build the prism Pa, thus achieving a low-profile optical system as a whole.
The display light beam 154 that leaves the focal plane 156 as a diverging light beam is incident on a half mirror 152 defined by a parabolic surface while being totally reflected between the flat surfaces 157 and 158, and is reflected by the half mirror surface 152. At the same time, the light beam 154 forms an enlarged virtual image of the displayed image by the refractive power of the half mirror surface 152, and becomes a nearly collimated light beam. The light beam is transmitted through the surface 157 and enters a pupil 153 of the observer, thus making the observer to recognize the displayed image.
On the other hand, an object light beam 155 coming from an outer field is transmitted through a surface 158b that builds a prism Pb, is transmitted through the half mirror 152 defined by the parabolic surface, and is transmitted through the surface 157 to enter the pupil 153 of the observer. The observer visually observes the displayed image that overlaps the landscape of the outer field.
In this reference as well, the displayed image is observed and an object image can also be recognized by the arrangement similar to that in U.S. Pat. No. 4,775,217.
Furthermore, Japanese Patent Application Nos. 7-65109 and 7-123256 disclose a zoom optical system which has a plurality of transparent optical elements, each of which is formed integrally with a plurality of refracting surfaces and a plurality of reflecting surfaces, so that a light beam enters the transparent optical element from one refracting surface, and leaves externally from another refracting surface after it is repetitively reflected by the plurality of reflecting surfaces. Also, an image sensing device which forms an image on a solid-state image sensing element using such an optical system is disclosed in Japanese Patent Application Nos. 7-65104, 7-65106, 7-65107, 7-65108, and 7-65111.